stoichiometry problem

Question

HCl + Na2SO4 → NaCl + H2SO4

-If you start with 20.0 grams of hydrochloric acid, how many grams of sulfuric acid will be produced assuming there is 0% error?
-How many moles of sulfuric acid should be produced if you use 0.80 grams of sodium sulfate?
-How many formula units of sodium chloride are produced if you start with 6.43 moles of sodium sulfate?

Answer 1

Hi Kelani,

The reaction equation HCl + Na₂SO₄ → NaCl + H₂SO₄ gives us the ratios in which molecules are used up and produced in the reaction.  Based on this reaction, for every 1 mole of HCl and 1 mole of Na2SO4 we add together, we produce 1 mole of NaCl and one mole of H₂SO₄. The reaction equation gives us the mole ratios, but the question only gives us the mass, so we need to convert from mass to moles.

 

-If you start with 20.0 grams of hydrochloric acid, how many grams of sulfuric acid will be produced assuming there is 0% error?

1) Convert 20.0 g HCl to moles of HCl.

To do this, we first need to determine the molecular mass of HCl.  We do this by adding the atomic masses of the elements that make up the molecule.

H= 1.008g/mol

Cl = 35.435g/mol

HCl = 36.443 g/mol

This tells us that one mole of HCl weighs 36.443 g.

We can determine the number of moles of a substance we have by dividing the total mass by the molecular mass of the substance.  In this case;

20.0 g HCl / 36.443g/mol = 0.549 moles HCl.

 

2) Use the number of moles of HCl used to determine the number of moles of sulfuric acid produced.

Based on our reaction equation, we know that 1 mole of sulfuric acid is produced for each mole for HCL used, so 0.0549 moles HCl * 1mole H₂SO₄/1moleHCL = 0.549 moles H₂SO₄.

 

3) Convert the number of moles of H₂SO₄ into grams.

Once again, we need to calculate the molecular mass.

Based on the formula, we have 2 H, 1 S and 4 O

H=1.008 g/mol

S=32.065 g/mol

O=15.9994 g/mol

So our molecular mass = 2(1.008g/mol) + 32.065g/mol + 4(15.9994g/mol) = 98.0786 g/mol

So 1 mole of H₂SO₄ weighs 98.078g.

If we know the number of moles, we can multiply that by the atomic mass to determine the mass.

0.0549 moles H2SO4 x 98.078 g/mol = 53.84 g H₂SO₄

 

-How many moles of sulfuric acid should be produced if you use 0.80 grams of sodium sulfate?

1) Convert g Na₂SO₄ to moles Na₂SO₄.

Molecular weight Na₂SO₄ =

Na=22.990

S=32.065 g/mol
O=15.9994 g/mol

So our molecular mass = 2(22.990g/mol) + 32.065g/mol + 4(15.9994g/mol) = 142.0426 g/mol

0.80g /142.0426g/mol = .0056 moles Na₂SO₄

 

2)Determine how many moles of H2SO4 will be produced.  The ratio of H₂SO₄ produced to Na₂SO₄ used is 1:1, so 0.0056 moles Na₂SO₄ x 1mole H₂SO₄/1mole Na₂SO₄ = 0.056 moles H₂SO₄.

 

3) Convert moles H₂SO₄ into g H₂SO₄

H=1.008 g/mol
S=32.065 g/mol
O=15.9994 g/mol
So our molecular mass = 2(1.008g/mol) + 32.065g/mol + 4(15.9994g/mol) = 98.0786 g/mol

0.0056 moles H₂SO₄ x 98.0786 g/mol = 0.55g H₂SO₄

 

-How many formula units of sodium chloride are produced if you start with 6.43 moles of sodium sulfate?

1) determine the number of moles of NaCl produced.

Based on the reaction equation, 1 mole of NaCl is produced for each mole of Na₂SO₄ used, so the ratio is 1:1.

6.43 moles Na₂SO₄ x 1 mole NaCl/1mole Na₂SO₄ = 6.43 moles NaCl.

 

2) Convert moles NaCl to formula units NaCl.

A formula unit is the lowest whole number ratio of atoms for a compound.  In this case, NaCl is the formula unit.  1 mole contains 6.02 x 10²³ formula units.

therefore, formula units of NaCl = 6.43 moles NaCl x 6.02x10²³ 

So, we have 3.82 x 10²⁴ formula units of NaCl.